What pattern(s) to use for this system ? HRIS/Payroll system

Hello!

I am currently working on a Human Resource Information System(HRIS)/Payroll system. Our professor only require us to use Strategy, Decorator and Observer patterns. Any ideas what pattern to be use, how can i implement that specific pattern in my system and can someone give me overview of that pattern .. I read one article that i can use decorator pattern in Request for leave of employees. can someone help me.

You can use the patterns as described by the professor but I'd probably also incorporate the Strategy pattern as well. I can give you some definitions of the patterns or try to simplify them but this could be a long answer to explain where and how to implement all the patterns. I know I wasn't much help but if you have specific questions maybe I can help.